1. Field of the Invention
The present invention relates to an apparatus for washing semiconductor wafers and others with chemical solution and water and drying them with dry air.
2. Description of the Related Art
The automatic washing apparatus is well-known as means for washing semiconductor wafers with chemical solutions. This automatic washing apparatus has plural processing sections where the semiconductor wafers can be washed with chemical solutions and water and then dried. More specifically, it includes ammonia-washing, water-washing, hydrofluoric-acid-washing and drying vessels so as to successively apply a series of processing steps to the semiconductor wafers, for example.
When the conventional washing apparatus is used to wash the semiconductor wafers, a plurality of the semiconductor wafers (or 25 sheets of them, for example) are housed in a cassette and they are immersed together with the cassette in chemical solutions in chemical washing vessels. The wafer cassette is then pulled out of the chemical washing vessel, washed with water and dried. In the case, wafer cassette may be dipped in heated chemical solution or heated water.
The wafer cassette is made of fluorine system resin (Trade Mark PFA). This resin is excellent in acid resistance and alkali resistance. However, the wafer cassette is complicated in shape and large in surface area. having a plurality of grooves to hold the wafers therein. When it is repeatedly immersed into alkali and acid, therefore, its material (or fluorine system resin) permeates little by little into the chemical solutions, and dissolves then in the solutions, thereby deteriorating to contaminate them in the processing vessels.
Semiconductor devices have been more highly integrated and their circuit patterns have been made finer and finer these days. When the chemical solutions are deteriorated by the contamination, their capacity of washing the semiconductor wafers is lowered, thereby disturbing the formation of super-fine patterns on each of the wafers. When a great many semiconductor wafers each having super-finely patterned chips are to be processed, therefore, the chemical solutions in the vessels must be replaced by new ones for a short time.